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From Wikipedia, the free encyclopedia
In number theory, a bi-twin chain of length k + 1 is a sequence of natural numbers
in which every number is prime.[1]
The special case, when the four numbers are all primes, they are called bi-twin primes,[2] such n values are
Except 6, all of these numbers are divisible by 30.
The numbers form a Cunningham chain of the first kind of length , while forms a Cunningham chain of the second kind. Each of the pairs is a pair of twin primes. Each of the primes for is a Sophie Germain prime and each of the primes for is a safe prime.
k | n | Digits | Year | Discoverer |
---|---|---|---|---|
0 | 3756801695685×2666669 | 200700 | 2011 | Timothy D. Winslow, PrimeGrid |
1 | 7317540034×5011# | 2155 | 2012 | Dirk Augustin |
2 | 1329861957×937#×23 | 399 | 2006 | Dirk Augustin |
3 | 223818083×409#×26 | 177 | 2006 | Dirk Augustin |
4 | 657713606161972650207961798852923689759436009073516446064261314615375779503143112×149# | 138 | 2014 | Primecoin (block 479357) |
5 | 386727562407905441323542867468313504832835283009085268004408453725770596763660073×61#×245 | 118 | 2014 | Primecoin (block 476538) |
6 | 263840027547344796978150255669961451691187241066024387240377964639380278103523328×47# | 99 | 2015 | Primecoin (block 942208) |
7 | 10739718035045524715×13# | 24 | 2008 | Jaroslaw Wroblewski |
8 | 1873321386459914635×13#×2 | 24 | 2008 | Jaroslaw Wroblewski |
q# denotes the primorial 2×3×5×7×...×q.
As of 2014[update], the longest known bi-twin chain is of length 8.
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